[Testing Platform] Batch Filter

This would work alongside #3527.

A filter type that could specify a start index and an end index, and pass that filter through to test adapters.

Test adapters could implement this and skip/batch as appropriate. All the testing platform needs to do is pass through a new filter type with the start/end indexes on it.

This would enable users/build systems to run batches of tests on different processes/agents to speed up test runs using parallelism.

Logic could be as follows:

--dotnet run --count-tests

500

dotnet run --batch-filter 0 99
dotnet run --batch-filter 100 199
dotnet run --batch-filter 200 299
dotnet run --batch-filter 300 399
dotnet run --batch-filter 400 499

public sealed class BatchFilter : ITestExecutionFilter
{
    public required int StartIndex { get; init; }
    public required int EndIndex { get; init; }
}

Read this issue alongside #3527 and trace how the testing platform passes execution filters to test adapters. Check the command-line handling for --batch-filter and the adapter filter interfaces first. Done means the platform accepts start and end indexes, forwards them to adapters, and supports the example batch invocations without breaking existing filters.